The "channel" notion is that a sensory pathway functions as though it contained several rather independent information-processing channels, each sensitive to a different feature of the stimulus. Some "channels" correspond to the known feature-filtering properties of single neurons. We propose to use the "channel" approach to refine existing diagnostic tests and to develop new tests that will be more sensitive and diagnostically more specific than current tests. With amblyopic infants and where psychogenic disorder is suspected we will test channels objectively by applying new evoked potential techniques. We will follow-up our preliminary finding that double-flash campimetry detects glaucoma before field changes occur, and find whether improved psychophysical tests can aid the diagnosis of multiple sclerosis (MS). We will test whether some MS patients with abnormal grating contrast sensitivity experience difficulty in recognizing objects. We will compare color modulation tests with conventional color vision tests in diabetes and retrobulbar neuritis.